So i want to naturally carbonate my beer instead of force carbonating it. I'd like to use beer tools to determine how much wort to set aside to yield me my desired volumes of CO2. I don't know of any way to work what the 'priming agent rate' is for my wort is… I know that for it to be right, you'll have to factor in the original gravity and the terminal gravity…

Has anyone here figured this out? Is there a calculator I don't know of in BeerTools?

You need to guess at your FG, and set aside some wort based on that estimated gravity change. Then, when your beer is finished, subtract the FG from the OG, to get the fermentable gravity. Then, knowing that 37 gravity points/gallon is equivalent to 1# of corn sugar, you can use the BTP carbonation calculator then convert # of sugar to volume of wort.